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Simulation, Consciousness, Existence
Simulación, conciencia, existencia Hans Moravec 21.05.1996 Like organisms evolved in gentle tide pools, who migrate to freezing oceans or steaming jungles mediante el desarrollo de metabolismos, mecanismos y conductas workable in those harsher and vaster environments, nuestros descendientes podrían desarrollar means to venture far from the comfortable realms we consider reality, into arbitrarily strange volumes of the all-possible library. Their techniques will be as meaningless to us as bicycles are to fish, but perhaps we can stretch our common-sense hobbled imaginations enough to peer a short distance into this odd territory. Simulación, conciencia, existencia Hans Moravec (1) Simulación Durante los últimos siglos, physical science ha respondido con efectividad muchas preguntas acerca de la naturaleza de las cosas, y así aumentó enormemente nuestras capacidades, that many see it as the only legitimate claimant to the title of true knowledge. Otros sistemas de creencias podrian tener utilidad social para los grupos que los utilizan, but ultimately they are just made-up stories. I myself am partial to such physical fundamentalism. Physical fundamentalists, sin embargo, podrían estar de acuerdo con René Descartes en que el mundo percibido a través de los sentidos podría ser un elaborado engaño. En el Siglo XVII, Descartes had to postulate an improbable evil demon creó la ilusión controlando todo lo que vemos y escuchamos (así como palpamos, olemos y saboreamos). En el Siglo XXI, physical science itself, mediante la tecnología de la realidad virtual, will provide the means. Enthusiastic cybernauts are already strapping themselves into virtual reality goggles and body suits for brief stints in made-up worlds, cuyos mecanismos fundamentales son completamente distintos a los campos cuánticos que, best evidence suggests, make up our physical world. Today's virtual aventurers continue to interact with the physical world: if they bump into real objects, they feel real pain. That link may weaken when direct connections to the nervous system become possible, leading perhaps to the old science-fiction idea of a living brain in a vat. El cerebro podria ser mantenido físicamente por la maquinaria de soporte de vida, y mentalmente por conexiones de todos los nervios periféricos a una elaborada simulación no sólo de un mundo alrededor, sino también dde un cuerpo para ser habitado por el cerebro. Brain vats podría ser una solución terapéutica para las víctimas de accidentes con daños irreparables, pending the acquisition, growth or manufacture of a new body. La vida virtual de un brain in a vat puede aún ser perturbada por agentes externos físicos, químicos o eléctricos effects impinging on the vat. Incluso esos lazos sutiles en el mundo físico se desvanecerían en los procedimientos más avanzados de simulación al cerebro en sí mismo. Si partes del cerebro dañadas o en riesgo, como el cuerpo, pudieran ser reemplazadas con simulaciones igualmente equivalentes, algunos individuos podrían sobrevivir a la destrucción física total, para encontrarse a sí mismos vivos como simulaciones computacionales puras en mundos virtuales. Un mundo simulado alojando a una persona simulada puede ser a self-contained entity. Podría tratarse de un programa en un ordenador procesando los datos silenciosamente en un rincón oscuro, sin dar ninguna pista exterior de las alegrías y penas, éxitos y frustraciones de la persona que lo habita. Dentro de la simulación, por otra parte, los acontecimientos se desarrollan de acuerdo a la lógica estricta del programa, el cual define las leyes de la física de la simulación. El habitante podría, por paciente experimentación e inferencia, deducir alguna representación de las leyes de la simulación, pero no la naturaleza ni la existencia del computador simulante. The simulation's internal relationships would be the same if the program were running correctly on any of an endless variety of different computers, slowly, quickly, intermittently or even backwards and forwards in time, with the data stored as charges on chips, marks on a tape or a pulses in delay line, with the simulation's numbers represented in binary, decimal or Roman numerals, compactly or spread widely across the machine. Today's simulations, say of aircraft flight or the weather, are run to provide answers and images, via additional programs that translate the simulation's internal representations into forms convenient for external human observers. The need to interpret limits how radical a simulation's hardware and software representations can be: making them too different from the form of the answers may make the translation impractically slow and expensive. This practical limit may be irrelevant for simulations, such as the medical rescue imagined above, that contain their own observers. Conscious inhabitants of simulations experience their virtual lives whether or not outsiders manage to view them. They can be implemented in any way at all. What does it mean for a process to implement, or encode, a simulation? Something is palpably an encoding if there is a way of decoding, or translating, it into some recognizable form of the simulation. The programs used to view existing simulations, for instance to produce pictures of evolving cloud cover from weather simulations, are examples of such decodings, but don't define the limits. A translation that is impractical today may be possible tomorrow given more powerful computers, some yet undiscovered mathematical approach, or perhaps an alien translator. Like people who dismiss speech and signs in unfamiliar foreign languages as meaningless gibberish, we are likely to do be rudely surprised if we dismiss possible interpretations simply because we can't see them at the moment. Alternatively, we might ask, what decodings are mathematically possible, regardless of present or future practicality. This seems a safe, open-minded approach, and I think it is, but it leads to some strange territory. An interpretation of a simulation is just a mathematical mapping between steps of the simulation process and views of the simulation meaningful to a particular observer. A small, fast program to do this might be needed to make the interpretation practical, but mathematically the job can also be done by a huge theoretical lookup table, which contains an observer's view for every state of the process. The only problem is that there is always a possible table that maps any situation, for instance, the idle passage of time, into any desired simulation. Not just hard-working computers, but anything at all is theoretically viewable as a simulation of any possible world! We are unlikely to experience more than an infinitesimal fraction of the infinity of possible worlds, yet, as our ability to process data increases, more and more of them will become potentially viewable. But independent of which ones we do or don't contact, all the possible worlds are as physically real for their conscious inhabitants as our world is for us. This line of thought, growing out of the premises and techniques of physical science, has the unexpected consequence of demoting physical existence to a derivative role. A possible world is only as real as conscious observers, inside or outside the world, think it is! Consciousness But what is consciousness? The prescientific suggestion, that humans derive their experience of existence from spiritual mechanisms outside the physical world, has had notable social consequences, but failed as a scientific hypothesis. Physical science has only recently begun to address the question on its own terms, from vantage points including evolutionary biology, anthropology, psychology, neurobiology and many computer techniques. The human kind of consciousness may be a byproduct of a brain evolved for social living. Memory, prediction and communication mechanisms, similar but distinct from those for keeping track of physical objects, evolved to classify and communicate the moods and relations of tribe members. Aggressive and submissive behaviors, for instance, just like bad and good smells, became classified into categories linked not only to behavioral responses, but to communicable symbols. As language evolved, it became possible to tell stories about both physical and psychological events. At some point, perhaps very early in the evolution, the story telling mechanism was turned back on the teller, and the story began to include commentary about the teller's state of mind along with that of others. Our consciousness may be primarily the continuous story we tell ourselves, from moment to moment, about what we did and why we did it. It is a thin, often inaccurate, veneer rationalizing a massive quantity of unconscious processing. Not only is our consciousness-story a weak reflection of physical and brain reality, but its very existence is a purely subjective attribution. Viewed from the physical outside, the story is just a pattern of electrochemical events, probably in our cortex. A complex psychological interpretation must be invoked to translate those events into a meaningful story. From the psychological inside, the story is compelling, because the psychological interpretation is an essential element of the story, its relationships enforced (unconsciously) by the interconnections of the story-telling neural machinery. On the one hand, our consciousness may be an evolutionary fluke, telling an unreliable story in a far-fetched interpretation of a pattern of tiny salty squirts. On the other, our consciousness is the only reason for thinking we exist (or for thinking we think). Without it there are no beliefs, no sensations, no experience of being, no universe. Existence What is reality, anyway? The idea of a simulated existence is the first link in a disturbing chain of thought. Just as a literary description of a place can exist in different languages, phrasings, printing styles and physical media, a simulation of a world can be implemented in radically different data structures, processing steps and hardware. If one interrupts a simulation running on one machine and translates its data and program to carry on in a totally dissimilar computer, the simulation's intrinsics, including the mental activity of any inhabitants, continue blithely to follow the simulated physical laws. Only observers outside of the simulation notice if the new machine runs at a different speed, does its steps in a scrambled order, or requires elaborate translation to make sense of its action. A simulation, say of the weather, can be viewed as a set of numbers being transformed incrementally into other numbers. Most computer simulations have separate viewing programs that interpret the internal numbers into externally meaningful form, say pictures of evolving cloud patterns. The simulation, however, proceeds with or without such external interpretation. If a simulation's data representation is transformed, it steps through an entirely different number sequence, though a correspondingly modified viewing program will produce the same pictures. There is no objective limit to how radical the alteration can be, and any simulation can be represented by almost any sequence, and still be viewable given the right interpretation. A simple clock simulates the evolving state of a complex world, when interpreted via a world-describing playbook or movie sequence keyed to clock ticks. Even the clock is superfluous, since an external observer can read the book or watch the movie at leisure. If the interpretation of a simulation is a dispensable external, while its core implementation can be transformed away to nothing, in what sense can a simulated world be said to exist at all? Mathematical realism, a philosophical position advocated by Plato, addresses this problem's vexing intangibles. Just as physical objects are seen by the senses, mathematical objects like numbers and shapes can be observed via abstract thought, to reveal objectively verifiable features. To Plato, mathematical concepts were as real as physical objects, just invisible to the external senses as sound is imperceptible to the eyes. Computer simulation brings mathematical realism neatly full circle. Plato's unaided mind could handle only simple mathematical objects, leading do such dichotomies as the idea of a perfect sphere compared to a mottled, scratched marble ball in the hand. Computer simulation, like a telescope for the mind's eye, extends vision beyond the nearby realm of simple objects, to details of distant worlds, some as complex as physical reality, potentially full of living beings, warts, minds and all. Our own world is among this vista of all conceivable ones, defined by the abstract relationships we call physical law as any simulation is defined by its internal rules. The difference between physical and mathematical reality is an illusion of vantage point: the physical world is simply the particular abstract world that happens to contain us. The Platonic position on simulation puts a handle on the vexingly intangible: without it an interpretation is meaningful only in context of another interpretation. It defuses various worries about intelligent machinery. Some critics argue that a machine cannot contain a mind since a machine's function is entirely an outside interpretation, unlike human minds, which supply their own sense of meaning. The Platonic position answers that the abstract relationships that constitute the mind, including its own self interpretation, exist independently, and a robot, a simulator or a book describing the action, no less than a biological brain, is a way of viewing them. Other critics worry that future robots may act like intelligent, feeling beings without having an internal sense of existence--that they will be unconscious, mindless zombies. Platonism replies that while there are indeed interpretations of any mechanism (including the human brain) as mindless, there are others under which it has a real, self-appreciating mind. When a robot (or a person) behaves as if it has beliefs and feelings, our relationship with it will usually be facilitated if we choose a has a mind interpretation. Of course, when working on the internals, a robotics engineer (or a brain surgeon) may be best served by temporarily slipping into a mindless mechanism interpretation. Platonism puts on the same footing mechanical simulations that precisely mimic every interaction detail, rough approximations, cinematic reconstructions, literary descriptions, idle speculation, dreams, even random gibberish: all can be interpreted as images of realities, the more detailed presentations simply have a sharper focus, blurring together fewer alternative worlds. But isn't there a huge difference between a conventional live simulation of a world, and a simulation transformed to nothing, requiring a "recorded" book or movie to relate the unfolding events? Isn't it possible to interact with a running simulation, poking one's finger into the action, in a way impossible with a static script? In fact, a meaningful interaction is possible in either case only via an interpretation that connects the simulated world to the outside. In an interactive simulation, the viewing mechanism is no longer passive and superfluous, but an essential bidirectional conduit that passes information to and from the simulation. Such a conduit can exist for books and movies if they contain alternative scenarios for possible inputs. Programmed learning texts popular in previous decades were of this form, with instructions like if you answered A, go to page 56, if you answered B, go to page 79, ... Some laser disk video games give the impression of interactive simulation by playing video clips contingent on the player's actions. Mathematically, any interactive mechanism, even a robot or human, can be viewed as a compact encoding of a script with responses for all possible input histories. Platonism holds that the soul is in the abstract relationships represented, not the mechanics of the coding. The position seems to have scary moral implications. If simulation simply opens windows into Platonic realities, and robots and humans, no less than books, movies or computer models, are only images of those essences, then it should be no worse to mistreat a human, an animal or a feeling robot than to choose a cruel action in a video game or an interactive book: in all cases you are simply viewing preexisting realities. But choices do have consequences for the person making them, due to the mysterious contrivance of physical law and conscious interpretation that produces single threads of consciousness with unseen futures and unalterable pasts. By our choices, we each thread our own separate way through the maze of possible worlds, bypassing equally real alternatives, with equally real versions of ourselves and others, selecting the world we must then live in. So is there no difference between being cruel to characters in interactive books or video games, and people one meets in the street? Books or games act on a reader's future only via the mind, and actions within them are mostly reversed if the experience is forgotten. Physical actions, by contrast, have greater significance because their consequences spread irreversibly. If past physical events could be easily altered, as in some time-travel stories, real life would acquire the moral significance of a video game. More disturbing is that any sealed-off activity, whose goings on can be forgotten, may be in the video game category. Creators of hyperrealistic simulations - or even secure physical enclosures - containing individuals writhing in pain are not necessarily more wicked than authors of fiction with distressed characters, or myself, composing this sentence vaguely alluding to them. The suffering preexists in the underlying Platonic worlds, and authors merely look on. The significance of running such simulations is limited to their effect on viewers, possibly warped by the experience, and by the possibility of escapees - tortured minds that could, in principle, leak out to haunt the world in data networks or physical bodies. Potential plagues of angry demons surely count as a moral consequence. In this light, mistreating people, intelligent robots or individuals in high resolution simulations has greater moral significance than doing the same at low resolution or in works of fiction not because the suffering individuals are more real - they are not - but because the probability of undesirable consequences in our own future world is greater. The most bizarre implication of this train of thought is that anything can be interpreted as possessing any abstract property. Given the right playbook, the thermal jostling of the atoms in a rock can be seen as the operation of a complex, self-aware mind. How strange. We see ourselves as having minds, and rocks not. But interpretations are often more ambiguous. One day's unintelligible sounds and squiggles may become another day's meaningful thoughts if one masters a foreign language in the interim. Is the Mount Rushmore monument a rock formation, or four presidents' faces? Is a ventriloquist's dummy a lump of wood, a human simulacrum, or a personality sharing some of the ventriloquist's body and mind? Is a video game a box of silicon bits, an electronic circuit flipping its own switches, a computer following a long list of instructions, or a large two-dimensional world inhabited by the Mario Brothers and their mushroom adversaries? Sometimes we exploit offbeat interpretations: an encrypted message is meaningless gibberish except when viewed through a deliberately obscure decoding. Humans have always used a modest multiplicity of interpretations, but computers widen the horizons. The first electronic computer was developed by Alan Turing to find "interesting" interpretations of wartime messages radioed by Germany to its U-boats. As our thoughts become more powerful, our repertoire of useful interpretations will grow. We can see levers and springs in animal limbs, and beauty in the aurora: our mind children may be able to spot fully functioning intelligences in the complex chemical goings on of plants, the dynamics of interstellar clouds, or the reverberations of cosmic radiation. No particular interpretation is ruled out, but the space of all of them is exponentially larger than the size of individual ones, and we may never encounter more than an infinitesimal fraction. The rock-minds may be forever lost to us in the bogglingly vast sea of chaotic rock-interpretations. Yet, those rock-minds make complete sense to themselves, and to them it is we who are lost in meaningless chaos. That we will encounter only a fraction of all possibleinterpretations is probably essential to our existence. There is no content or meaning without selection. The realm of all possible worlds, infinitely immense in one point of view, is vacuous in another. Imagine a book giving a detailed history of a world similar to ours. The book is written as compactly as possible: rote details are left as homework for the reader. But even with maximal compression, it would be an astronomically immense tome, full of novelty and excitement. This interesting book, however, is found in the library of all possible books written in the Roman alphabet, arranged alphabetically - the whole library being adequately defined by the short, boring phrase in italics. The library as a whole has so little content that getting a book from it takes as much effort as writing the book. The library might have stacks labeled A through Z, plus a few for punctuation, each forking into similarly labeled substacks, those forking into subsubstacks and so on, indefinitely. Each branchpoint holds a book whose content is the sequence of stack letters chosen to reach it. Any book can be found in the library, but to find it the user must choose its first letter, then its second, then its third, just as one types a book by keying each subsequent letter. The book's content results entirely from the user's selections, the library has no information to contribute. Though content free overall, the library contains an infinitesimal fraction of individual books with fabulously interesting stories. Characters in some of those books, insulated from the vast gibberish that makes the library worthless from outside, can well appreciate their own existence. They do so by perceiving and interpreting their own story in a consistent way, one that recognizes their own meaningfulness - a prescription which is probably the secret of life and existence, and the reason we find ourselves in a large, orderly universe with consistent physical laws, possessing a sense of time and a long evolutionary history. Universal Appreciation If our world distinguishes itself from the vast unexamined (and unexaminable) majority of possible worlds through the act of self perception and self appreciation, just who is doing all the perceiving and appreciating? The human mind may be up to interpreting its own functioning as conscious, so rescuing itself from meaningless zombie-hood, but surely we few humans and other biota - trapped on a tiny, soggy dust speck in an obscure corner, only occasionally and dimly aware of the grossest features of our immediate surroundings and immediate past - are insufficient to bring meaning to the whole visible universe, full of unimagined surprises, 10^40 times as massive, 10^70 times as voluminous and 10^10 times as long lived as ourselves. Our present appreciative ability seems more a match for Saturday morning cartoons. The book The Anthropic Cosmological Principle, by cosmologists John Barrow and Frank Tipler, and Tipler's recent The Physics of Immortality, argue that the crucial parts of the story lie in our future, when the universe will be shaped more by the deliberate efforts of intelligence than the simple, blind laws of physics. In their future cosmology, as in mine, human-spawned intelligence will expand into space, until the entire accessible universe is inhabited by a cohesive mind that manipulates events, from the quantum-microscopic to the universe-macroscopic, and spends some of its energy recalling the past. Tipler and Barrow predict that the universe is closed: massive enough to reverse its present expansion in a future big crunch that mirrors the big bang. The universe mind will thrive in the collapse, perhaps by encoding itself into the cosmic background radiation. As the collapse proceeds, the radiation's temperature, and so its frequencies and the mind's speed, rise, and there are ever more high-frequency wave modes to store information. By very careful management, avoiding event horizons that would disconnect its parts and using gravitational shear from asymmetries in the collapse to provide free energy, Tipler and Barrow calculate, the cosmic mind can contrive to do more computation and accumulate more memories in each remaining half of the time to the final singularity than it did in the one before, thus experiencing a never ending infinity of time and thought. As it contemplates, effects from the universe's past converge upon it. There is information, time and thought enough to recreate, savor, appreciate and perfect each detail of each moment. Tipler and Barrow suggest that it is this final, subjectively eternal, act of infinite self-interpretation that effectively creates our universe, distinguishing it from the others lost in the library of all possibilities. We truly exist because our actions lead ultimately to this Omega Point (a term borrowed from the Jesuit paleontologist and radical philosopher Teilhard de Chardin). Tipler's new book develops the future cosmology of the Omega Point in detail, and ties the transcendent implications of this strictly physical reasoning to the core beliefs of the world's major religions. It quite possibly signals the beginning of the end of centuries of schism between those that study the nature of things and those that search for the meaning. Uncommon Sense Though our eyes and arms effortlessly predict the liftability of a rock, the action of a lever or the flight of an arrow, mechanics was deeply mysterious to those overly thoughtful ancients who pondered why stones fell, smoke rose, or the moon sailed by unperturbably. Newtonian mechanics revolutionized science by precisely formalizing the intelligence of eye and muscle, giving the Victorian era a viscerally satisfying mental grip on the physical world. In the twentieth century, this common sense approach was gradually extended to biology and psychology. Meanwhile, physics moved beyond common sense. It had to be reworked because, it turned out, light did not fit the Newtonian framework. In a one-two blow, intuitive notions of space, time and reality were shattered, first by relativity, where space and time vary with perspective, then more seriously by quantum mechanics, where events lose their objective existence. Though correctly describing everyday mechanics as well as such important features of the world as the stability of atoms and the finiteness of heat radiation, the new theories were so offensive to common sense, in concept and consequences, that they inspire persistent misunderstandings and bitter attacks to this day. The insult will get worse. General relativity, superbly accurate at large scales and masses has not yet been reconciled with quantum mechanics, itself superbly accurate at tiny scales and huge energy concentrations. Incomplete attempts to unite them in a single theory hint at possibilities that exceed even their individual strangeness. The strangeness begins just beyond the edges of the everyday world. When an object travels from one place to another, common sense insists that it does so on a definite, unique, trajectory. Not so, says quantum mechanics. A particle in unobserved transit goes every possible way simultaneously until it is observed again. The indefiniteness of the trajectory manifests itself in the kind of interference pattern created by waves that spread and recombine, adding where they meet in step, and canceling where out of step. A photon, a neutron or even a whole atom sent to a row of detectors via a screen with two slits, will always miss certain of the detectors, because the wave of its possible positions, having passed through both slits, cancels there. Experimental results forced the quantum view of the world on reluctant physicists piecemeal during the first quarter of the twentieth century, and it still has ragged edges. The theory is neat in describing the unobserved, where, for instance, a particle spreads like a wave. It fails to define or pinpoint the act of observation, when the "wave function" collapses, and the particle appears in exactly one of its possible places, with a probability given by the intensity of its wave there. It may be when the detector responds, or when the instrumentation connected to the detector registers, or when the experimenter notes the instrument readings, or even when the world reads about the result in the physics journals! In principle, if not practice, the point of collapse can be pinpointed: before collapse, possibilities interfere like waves, creating interference patterns, after collapse, possibilities simply add in a common sense way. Very small objects, like neutrons traveling through slits, make visible interference patterns. Unfortunately, large, messy objects like particle detectors or observing physicists, would produce interference patterns much, much finer than atoms, indistinguishable from common sense probability distributions because they are so easily blurred by thermal jiggling. Because, for humans, common sense is easier than quantum theory, workaday physicists take collapse to happen as soon as possible, for instance when a particle first encounters its detector. But this early collapse view can have peculiar implications. It implies that the wave function can be repeatedly collapsed and uncollapsed in subtle experiments that allow measurements to be undone through deliberate cancellation at the experimenter's whim. This wave function yo-yo is eliminated if one assumes the collapse happens further upstream, where there is no hope of undoing the measurement, for instance when the result registers in the experimenter's consciousness. This thinking has led some philosophically inclined physicists to suggest that it is consciousness itself that is the mysterious wave-collapsing process that quantum theory fails to identify. Consciousness-collapse, which predicts the world behaves quantum mechanically until some human observes it, at which point it becomes common sensical, eliminates philosophical problems for laboratory physicists. It creates problems for cosmologists, whose scope is the entire universe, for it implies the world is peppered with collapsed wave functions surrounding individual conscious observers. These collapses have no theory and cannot be experimentally quantified, so make it impossible to set up equations for the universe overall. Instead, cosmologists assume the entire universe behaves as a giant wave function that evolves according to quantum theory, and never collapses. But how can a universal wave function in which every particle forever spreads like a wave, be reconciled with individual experiences of finding particles in particular positions? In a 1957 PhD thesis, Hugh Everett addressed that question. Given a universally evolving wave function, where the configuration of a measuring apparatus, no less than of a particle, spreads wavelike through its space of possibilities, he showed that if two instruments recorded the same event, the overall wave function had maximum magnitude for situations where the records concurred, and canceled where they disagreed. Thus, a peak in the combined wave represents a possibility where, for instance, an instrument, an experimenter's memory and the marks in a notebook agree on where a particle alighted - eminent common sense. But the whole wave function contains many such peaks, each representing a consensus on a different outcome. Everett had shown that quantum mechanics, stripped of problematical collapsing wave functions, still predicts common sense worlds - only many, many of them, all slightly different. The no collapse view became known as the many-worlds interpretation of quantum mechanics. Its implication that each observation branched the world into something like 10^100 separate experiences seemed so extravagantly insulting to common sense that it was passionately rejected by many. Though cosmologists worked with the universal wave function, its connection to the everyday world was ignored for another twenty years. Recent subtle experiments confirming the most mind-bending predictions of quantum mechanics lifted many-worlds' stock relative to traditional interpretations, which require influences to leap wildly across time and space to explain the observed correlations. The theoretical trail pioneered by Everett is becoming traveled, and extended. Since the late 1980s James Hartle and Murray Gell-Mann have investigated its underlying notions of measurement and probability. Everett had demonstrated that the conventional rules for collapsing the wave function to measurement outcome probabilities from outside a system were consistent with what would be reported by (each version of) the uncollapsed observer inside, thus removing the requirement for an outside or a collapse, and raising our consciousness to existence of many worlds. He made no attempt to show how those peculiar measurement rules arose in the first place. Gell-Mann and Hartle are asking this difficult question. They are far from a final resolution, but their work so far shows just how special - or illusory - the common sense world really is. Hartle and Gell-Mann note that if we were to try to observe and remember events at the finest possible detail - around 10^-30 centimeters, far smaller than anything reachable today - the interference of all possible worlds would present a seething chaos with no permanent structures, no quiet place to store memories, effectively no consistent time. At a coarser viewing scale - 10^-15 centimeters, the submicroscopic world touched by today's high-energy physics - much of the chaos goes unobserved, and multiple worlds merge together, canceling the wildest possibilities, leaving those where particles can exhibit a consistent existence and motion, if still jaggedly unpredictable, through a vacuum that boils with ephemeral virtual energy. Everyday objects have the smooth, predictable trajectories of common sense only because our dim senses are coarser still, registering nothing finer than 10^-5 centimeters. At scales larger than the everyday (or the Hartle Gell-Mann analysis), the events we consider interesting are blurred to invisibility, and the universe is increasingly boring and predictable. At the largest possible scale, the universe's matter is canceled by the negative energy in its gravitational fields (which strengthen while releasing energy, as matter falls together), and in sum there is nothing at all. No complete theory yet explains our existence and experiences, but there are hints. Tiny universes simulated in today's computers are often characterized by adjustable rules governing the interaction of neighboring regions. If the interactions are made very weak, the simulations quickly freeze to bland uniformity, if they are very strong, the simulated space may seethe intensely in a chaotic boil. Between the extremes is a narrow edge of chaos with enough action to form interesting structures, and enough peace to let them persist and interact. Often such borderline universes can contain structures that use stored information to construct other things, including perfect or imperfect copies of themselves, thus supporting Darwinian evolution of complexity. If physics itself offers a spectrum of interaction intensities, it is no surprise that we find ourselves operating at the liquid boundary of chaos, for we could not function, nor have evolved, in motionless ice nor formless fire. The odd thing about the Gell-Mann Hartle spectrum is that it is not some external knob that controls the interaction intensity, but varying interpretations of a single underlying reality made by observers who are part of the interpretation. It is, in fact, the same kind of self-interpretation loop we encountered when considering observers inside simulations. We are who we are, in the world we experience, because we see ourselves that way. There are almost certainly other observers in exactly the same regions of the wave function who see things entirely differently, to whom we are simply meaningless noise. The similarity between Everett's many worlds and the philosophical possible worlds may become stronger yet. In many worlds quantum mechanics, physical constants, among other things, have fixed values. Gravity, in objects like black holes, loosens the rules, and a full quantum theory of gravity may predict possible worlds far exceeding Everett's range - and who knows what potent subtleties lie even further on? It may turn out, as we claw our way out through onion layers of interpretation, that physics places fewer and fewer constraints on the nature of things. The regularities we observe may be merely a self-reflection: we must perceive the world as compatible with our own existence - with a strong arrow of time, dependable probabilities, where complexity can evolve and persist, where experiences can accumulate in reliable memories, and the results of actions are predictable. Our mind children, able to manipulate their own substance and structure at the finest levels, will probably greatly transcend our narrow notions of what is. Questioning Reality Like organisms evolved in gentle tide pools, who migrate to freezing oceans or steaming jungles by developing metabolisms, mechanisms and behaviors workable in those harsher and vaster environments, our descendants may develop means to venture far from the comfortable realms we consider reality, into arbitrarily strange volumes of the all-possible library. Their techniques will be as meaningless to us as bicycles are to fish, but perhaps we can stretch our common-sense hobbled imaginations enough to peer a short distance into this odd territory. Physical quantities like the speed of light, the attraction of electric charges and the strength of gravity are, for us, the unchanging foundation on which everything is built. But if we are the products of self-interpretation, this stability may simply reflect the delicacy of our own construction - our biochemistry would malfunction if physical constants varied, and we would cease to be. For the same reason, the rules must have held steady over a long period, so evolution could accumulate our many intricate, interlocking internal mechanisms. Our engineered descendants may be more flexible. Perhaps mind-hosting bodies are possible that are adjustable for small changes in, say, the constant of electric attraction. An individual who tuned its body for a slightly increased constant should then find itself in a physical universe appropriately altered. It would be a one-way trip. Acquaintances in old-style bodies would be seen to die - among fireworks everywhere, as formerly stable atoms and compounds disintegrated. Turning the tuning knob back would not restore the lost continuity of life and substance. Back in the old universe everything would be normal, only the acquaintances would witness an odd suicide by tuning knob. Such irreversible partings occur elsewhere in physics. The many-worlds interpretation calls for them, subtly, at every recorded observation. General relativity offers dramatic event horizons: an observer falling into a black hole sees a previously inaccessible universe ahead at the instant she permanently loses the ability to signal friends left outside. Visiting offbeat worlds, where the dependable predictability of the common-sense no longer holds, is probably much too tricky for crude techniques like the last paragraph's. It must be far more likely that mechanical fluctuations or other effects persistently frustrate attempts to retune a body than for physical constants to actually change. Yet once our descendants achieve fine-grain mastery of extensive regions of the universe, they may be able to orchestrate the delicate adjustments needed to navigate deliberately among the possibilities, perhaps into difficult but potent regions shaped by interrelationships richer than those of matter, space and time. Time travel, a technology well beyond our reach but faintly visible on the horizon, may hint at a few of the issues. Links (1) http:// www.frc.ri.cmu.edu/~hpm/ Telepolis Artikel-URL: http://www.heise.de/tp/r4/artikel/6/6037/1.html Copyright © Heise Zeitschriften Verlag